body{
    text-align: center;
    overflow-y: auto;
    overflow-x: auto;
    background-color: lightcyan;
}
a:link{text-decoration:none;   /* 指正常的未被访问过的链接*/
}
a{
    color: gray;
}

.nav{
    width: 100%;height: 10%;
    background-color: white;
    display: flex;
    justify-content: center;
    margin: 1px auto;
    text-align: center;
}
.box{
    width: 80%;height: 15%;
    background-color: white;
    margin: 1px auto;
}

.lesson_box{
    width: 80%;height: 70%;
    background-color: white;
    display: flex;
    justify-content: center;
    flex-wrap: wrap;
    margin: 1px auto;
}
.lesson{
    width: calc(25% - 2px);
    height: calc(50% - 5px);
    background-color: white;
    margin-left: 2px;
    margin-top: 5px;
    /*background-image: url("/img/lo.gif");*/
}
.lesson_img{
    width: calc(100%);height:calc(60%)
}
.lesson_p{
    height: calc(10%);
    font-size: 10px;
    margin-top: 0px;
    color: gray;
    /*text-align: center;*/
}
.p_button{
    margin-left: 10px;
}